[Collins] Collins ham gear redesign

[Dr. Gerald N. Johnson]

The audio phase shift circuit in the 32S is a high pass filter and at 
the frequency the capacitor leads and capacitor inductances make a half 
wave delay line it oscillates. There is a service bulletin on that 
adding a resistor in series with the control grid to snuff that RF 
oscillation but I didn't find that today. ASAB1004 covers that with a 
100 pf from grid to ground for KWM-2. I see the KWM-2 sometimes used a 
twin T feed back circuit in that oscilator but the high pass side of 
that could cause RF oscillation too. 32S-1 didn't have that last series 
resistor while the 32S-3A did from the factory.

On 7/8/2014 2:37 PM, Glen Zook wrote:
> The 6EA8 works very well to replace the 6U8 in the Collins S-Line except
> in the tone oscillator in the 32S- series transmitters and the KWM-2-
> series. For some reason, and I don't really know why, when the 6EA8 is
> used in that circuit there is often a problem with the starting of the
> tone or a very distorted tone. Occasionally, the 6EA8 works fine in
> certain units. However, more times than not, I have definitely had
> problems using the 6EA8 in the tone oscillator circuits. As such, I
> don't take a chance and always put a 6U8 in that circuit.
>
> Glen, K9STH
> website: http://k9sth.com
>
>
73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association